Non-invasive DNA is a method of prenatal screening that is performed at around 12-22 weeks, and no later than 26 weeks. This is because the purpose of the non-invasive DNA test is to detect whether the fetus has the three major chromosomal disorders, namely trisomy 21, trisomy 18, and trisomy 13, by taking peripheral venous blood from the mother and extracting the fetal DNA for sequencing. If there is a problem with the results of the non-invasive DNA test, an amniocentesis will need to be completed before 24 weeks. Non-invasive DNA test results are usually available in two weeks. If the non-invasive DNA test is performed beyond 26 weeks, the results will be available at 28 weeks and in the perinatal period, at which point the clinical guidance is not very meaningful. When doing the non-invasive DNA test, you should pay attention to the fact that although you do not need to fast, you can have your blood drawn after breakfast, but you should also try to avoid stimulating food and avoid strenuous exercise before the blood draw, you can sit still for more than 30 minutes before having your blood drawn, otherwise the results may be affected.